It was made in a free sculpting program called Sculptris. Made by the developers of ZBrush, Sculptris allows you do do many of the same things as that other program. However, there are a few things that can't be done in Sculptris. For example, you can't get anywhere near as high of a resolution to the sculpt as you can in ZBrush, making it incredibly difficult to make crisp, good-looking texture. Oh well. At least it has a very user-friendly interface and is relatively straightforward to use.